Method for manufacturing energy storage devices

Abstract

The present invention provides a method for manufacturing an energy storage device that is suitable for suppressing variations in welding depth caused by variations in the surface shape of the outer edge of the sealing plate during welding of the case body and sealing plate of the energy storage device. [Solution] The method for manufacturing an energy storage device includes a case body preparation step, a sealing plate preparation step, and a welding step. The prepared case body 10 has an opening on at least one side. The prepared sealing plate 20 has a first surface, a second surface on the opposite side, and an outer peripheral edge 23 surrounding the first and second surfaces, and has a groove 22g along the outer peripheral edge 23 on the second surface 22. The welding step includes irradiating a first laser beam between the outer peripheral edge 23 and the groove 22g of the sealing plate 20 with the sealing plate 20 mounted on the case body 10 with its first surface facing the case body 10 and closing the opening, and then irradiating a second laser beam (laser beam L2) at the boundary between the case body 10 and the sealing plate 20.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an electricity storage device.

Background Art

[0002] Japanese Unexamined Patent Application Publication No. 2018-202478 discloses a technique for laser welding a case body and a lid in a battery case for an in-vehicle lithium battery. In this technique, a laser from a light source is split by a predetermined branching optical system into a first laser and a second laser each having a specific cross-sectional shape, and then the two consecutive lasers are simultaneously irradiated to the vicinity of the butt interface between the edge portion of the opening of the case body and the lid. The first laser is irradiated along the butt interface to the vicinity of the butt interface on the case body. The second laser is irradiated along the butt interface to the vicinity of the butt interface on the lid. By such laser irradiation, the case body and the lid are welded at the butt interface.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of Invention

Problems to be Solved by the Invention

[0004] Meanwhile, the inventors of the present application intend to provide a method for manufacturing an electricity storage device that is suitable for suppressing variations in welding depth caused by variations in the surface shape of the outer peripheral end of the sealing plate, in the welding of the case body and the sealing plate of the electricity storage device.

Means for Solving the Problems

[0005] A method for manufacturing an energy storage device disclosed herein includes the steps of: preparing a case body having an opening on at least one side; preparing a sealing plate for closing the opening; and a welding step of laser welding the case body and the sealing plate with the sealing plate mounted on the case body so as to close the opening. The sealing plate prepared in the step of preparing the sealing plate has a first surface, a second surface opposite to the first surface, and an outer peripheral edge surrounding the first and second surfaces, and has a groove along the outer peripheral edge on the second surface. The welding step includes irradiating a first laser beam between the outer peripheral edge and the groove on the sealing plate with the sealing plate mounted on the case body with the first surface facing the case body so as to close the opening, and then irradiating a second laser beam at the boundary between the case body and the sealing plate.

[0006] According to the inventors' findings, in conventional welding techniques, when laser welding the case body and sealing plate in a battery case, variations in the welding depth at the welding point can occur due to variations in the surface shape of the outer edge of the sealing plate (the abutting surface with respect to the case body) (for example, occurring during punching). This variation tends to increase as the battery case becomes larger with increasing battery size. The irradiation of the first laser beam in the welding process of the above-described energy storage device manufacturing method is suitable for melting at least a portion of the outer edge surface of the sealing plate and for forming a melted and aggregated portion within the region from the outer edge to the groove of the sealing plate. By melting at least a portion of the outer edge surface, variations in the surface shape of the end face are reduced. At the same time, the molten portion created by the irradiation of the first laser beam within the region tends to aggregate and round due to the surface tension acting on the molten portion in that region. The irradiation of the second laser beam after the first laser beam is suitable for forming a welded area with suppressed variations in welding depth at the boundary between the case body and the sealing plate. Therefore, the above method for manufacturing an energy storage device is suitable for suppressing variations in welding depth caused by variations in the surface shape of the outer edge of the sealing plate during welding of the case body and the sealing plate. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic perspective view showing an example of an energy storage device. [Figure 2] Figure 2 is an exploded perspective view of the energy storage device shown in Figure 1. [Figure 3] Figure 3 is a flowchart showing an example of a method for manufacturing an energy storage device, which is one embodiment of the present invention. [Figure 4] Figure 4 is a partially enlarged cross-sectional view of the sealing plate prepared in the sealing plate preparation process. [Figure 5] Figure 5 is a partially enlarged cross-sectional view showing the first laser beam irradiation during the welding process of a method for manufacturing energy storage devices. [Figure 6] Figure 6 is a partially enlarged cross-sectional view showing the state after irradiation with the first laser beam during the welding process of the energy storage device manufacturing method. [Figure 7] Figure 7 is a schematic diagram of the irradiation spot of a ring-mode laser. [Figure 8] Figure 8 is a partially enlarged cross-sectional view showing the irradiation of the second laser beam during the welding process in the manufacturing method of an energy storage device. [Figure 9] Figure 9 is a partially enlarged cross-sectional view showing the state of irradiation with the second laser beam during the welding process in the energy storage device manufacturing method. [Figure 10] Figure 10 is an explanatory diagram regarding laser welding using a single laser irradiation. [Figure 11] Figure 11 shows an example of an optical system for splitting laser light. [Figure 12] Figure 12 shows another example of an optical system for splitting laser light. [Modes for carrying out the invention]

[0008] Embodiments of the technology disclosed herein will be described below with reference to the drawings. The embodiments described herein are not intended to limit the invention in any particular way. Each drawing is schematic and does not necessarily reflect the actual object. In addition, the same reference numerals are used for members and parts that perform the same function, and redundant descriptions are omitted where appropriate. In addition, in this specification, notations such as "X~Y" indicating a numerical range mean "X or more and Y or less" unless otherwise specified.

[0009] In this specification, "energy storage device" refers to a device that is rechargeable and dischargeable. Energy storage devices include batteries generally referred to as lithium-ion batteries and lithium secondary batteries, as well as batteries such as lithium polymer batteries and nickel-metal hydride batteries. A secondary battery refers to a battery in general that can be repeatedly charged and discharged by the movement of charge carriers between the positive and negative electrodes. Energy storage devices may use either a liquid electrolyte or a solid electrolyte. For example, a secondary battery may be a secondary battery using a so-called liquid electrolyte, or a so-called all-solid-state battery using a solid electrolyte. Energy storage devices also include capacitors such as electric double-layer capacitors and lithium-ion capacitors.

[0010] Figure 1 is a perspective view showing an energy storage device 100 manufactured by the energy storage device manufacturing method described later, which is one embodiment of the present invention. Figure 2 is an exploded perspective view of the energy storage device 100. The symbols F, Rr, L, R, U, and D in the drawings represent front, back, left, right, top, and bottom, respectively. In the following description, the thickness direction of the energy storage device 100 is defined as the X direction, the width direction perpendicular to the thickness direction is defined as the Y direction, and the vertical direction perpendicular to the width direction and the thickness direction is defined as the Z direction.

[0011] As shown in Figures 1 and 2, the energy storage device 100 comprises a case body 10, a sealing plate 20, an electrode body 30 (shown in Figure 2), a positive electrode terminal 40, a negative electrode terminal 50, and an electrolyte (not shown). In this embodiment, the energy storage device 100 is a lithium-ion secondary battery.

[0012] The case body 10 and the sealing plate 20 form the case C of the energy storage device 100. The case C is the housing for the energy storage device 100. In this embodiment, the case C has a flat and rectangular parallelepiped shape (e.g., square). The case C houses the electrode body 30 and the electrolyte. In this embodiment, the thickness of the case C (external dimension in the X direction) is, for example, 3 cm or more and 6 cm or less, the width of the case C (external dimension in the Y direction) is, for example, 30 cm or more and 50 cm or less, and the height of the case C (external dimension in the Z direction) is, for example, 6 cm or more and 20 cm or less. Such a relatively large case C is preferable for increasing the capacity of the energy storage device 100 because it can accommodate a relatively large electrode body 30 inside the case C.

[0013] As shown in Figure 2, the case body 10 is constructed in a substantially rectangular parallelepiped shape, and in this embodiment, it is a rectangular tubular bottomed case having an opening 10A. Specifically, the case body 10 has an edge end 10E at one end in the Z direction (upper end in the figure) that defines the opening 10A. The edge end 10E surrounds the opening 10A. The case body 10 also has a shape that extends in the Y direction.

[0014] The case main body 10 has a bottom surface 11, a pair of narrow side surfaces 12, 13, and a pair of wide side surfaces 14, 15. The narrow side surfaces 12, 13 and the wide side surfaces 14, 15 form the peripheral side surface of the case main body 10. In the case main body 10, the bottom surface 11 is located at the lower end in the Z direction (the end on the side opposite to the opening 10A). The bottom surface 11 has a short side extending in the X direction and a long side extending in the Y direction, and has a substantially rectangular shape spreading in the X direction and the Y direction. The narrow side surfaces 12, 13 each have a short side extending in the X direction and a long side extending in the Z direction, and have a substantially rectangular shape spreading in the X direction and the Z direction. The pair of narrow side surfaces 12, 13 face each other in the Y direction. The wide side surfaces 14, 15 each have a long side extending in the Y direction and a short side extending in the Z direction, and have a substantially rectangular shape spreading in the Y direction and the Z direction. The pair of wide side surfaces 14, 15 face each other in the X direction. The lower ends of the narrow side surfaces 12, 13 and the wide side surfaces 14, 15 in the Z direction are connected to the bottom surface 11. The upper end portions of the narrow side surfaces 12, 13 and the wide side surfaces 14, 15 in the Z direction constitute the edge end portion 10E of the case main body 10. Such a case main body 10 is made of metal. Examples of the constituent material of the case main body 10 include aluminum, aluminum alloys, iron, and iron alloys. From the viewpoint of achieving both weight reduction of the case main body 10 and required rigidity, the constituent material of the case main body 10 is preferably aluminum or an aluminum alloy containing aluminum as a main component.

[0015] The sealing plate 20 is a member that closes the opening 10A of the case main body 10. The sealing plate 20 closes the opening 10A by being welded to the edge end portion 10E of the case main body 10 over the entire circumference thereof. The sealing plate 20 is configured in a substantially rectangular plate shape (that is, it is a substantially rectangular flat plate-shaped member in a plan view), and has a shape and size capable of closing the opening 10A. Examples of the constituent material of the sealing plate 20 include aluminum, aluminum alloys, iron, and iron alloys. From the viewpoint of weight reduction of the case C, the constituent material of the sealing plate 20 is preferably aluminum or an aluminum alloy containing aluminum as a main component.

[0016] In the present embodiment, the sealing plate 20 has a gas discharge valve 20a. The gas discharge valve 20a is a thin-walled portion configured to rupture when the pressure inside the case C rises to a predetermined value or higher. Through this rupture of the gas discharge valve 20a, the gas inside the case C is discharged to the outside of the case C, and further pressure increase inside the case C is prevented or suppressed. The gas discharge valve 20a is arranged at the central portion of the sealing plate 20 in the Y direction.

[0017] The electrode body 30 (shown in Figure 2) is housed in the case C, or the case main body 10. The electrode body 30 has a positive electrode and a negative electrode. In the present embodiment, the electrode body 30 is a so-called wound electrode body. The electrode body 30 is formed by winding a laminate, in which a strip-shaped positive electrode and a strip-shaped negative electrode are stacked with a strip-shaped separator (not shown) interposed therebetween, in the longitudinal direction around a winding axis. Instead of such a configuration, the electrode body 30 may be a stacked electrode body in which square-shaped positive electrodes and square-shaped negative electrodes are stacked in a mutually insulated state.

[0018] In the present embodiment, the outer shape of the electrode body 30 is a flat shape. The electrode body 30 has a pair of curved portions and a pair of flat surfaces between the pair of curved portions. Such an electrode body 30 (wound electrode body) is housed inside the case C with its winding axis oriented along the Y direction. The pair of curved portions of the electrode body 30 face the bottom surface 11 and the sealing plate 20 of the case C, respectively. Instead of such a housing mode, the electrode body 30 may be housed inside the case C with its winding axis oriented along the Z direction.

[0019] The positive electrode of the electrode body 30 has a laminated structure of, for example, a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector is preferably a strip-shaped conductive metal foil. Examples of constituent materials for the positive electrode current collector include aluminum, aluminum alloy, nickel, and stainless steel, with aluminum being preferred. The positive electrode active material layer is, for example, provided in a strip shape along the longitudinal direction on at least one surface of the strip-shaped positive electrode current collector. The positive electrode active material layer includes a positive electrode active material capable of reversibly intercalating and releasing charge carriers, and a binder. The positive electrode active material is preferably a lithium transition metal composite oxide. Specific examples of such oxides include lithium cobalt composite oxide, lithium manganese composite oxide, lithium nickel composite oxide, lithium nickel manganese composite oxide, lithium nickel cobalt composite oxide, and lithium nickel cobalt manganese composite oxide. An example of the binder is polyvinylidene fluoride (PVDF). Furthermore, the strip-shaped positive electrode current collector has a portion at one end in its width direction (short direction) where the positive electrode active material layer is not laminated and is exposed. Multiple positive electrode tabs (part of the positive electrode current collector) are formed at predetermined intervals in the longitudinal direction of the positive electrode current collector in this exposed portion. In the electrode body 30 as a wound electrode body, multiple such positive electrode tabs are stacked to form a group of positive electrode tabs (not shown). The group of positive electrode tabs is located at one end of the electrode body 30 in the Y direction (left end in Figure 2) and is connected to the positive electrode current collector 31. Examples of materials used to construct the positive electrode current collector 31 include aluminum and aluminum alloys.

[0020] The negative electrode of the electrode body 30 has a laminated structure of, for example, a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector is preferably a strip-shaped conductive metal foil. Examples of constituent materials for the negative electrode current collector include copper, copper alloy, nickel, and stainless steel, with copper foil being preferred. The negative electrode active material layer is provided, for example, in a strip shape along the longitudinal direction on at least one surface of the strip-shaped negative electrode current collector. The negative electrode active material layer includes a negative electrode active material capable of reversibly intercalating and releasing charge carriers, and a binder. Examples of negative electrode active materials include carbon materials such as graphite and carbon. Examples of binders for the negative electrode active material include styrene-butadiene rubber (SBR) and carboxymethylcellulose (CMC). The strip-shaped negative electrode current collector also has a portion at one end in its width direction (short direction) where the negative electrode active material layer is not laminated and is exposed. Multiple negative electrode tabs (part of the negative electrode current collector) are formed on the exposed portion at predetermined intervals along the longitudinal direction of the negative electrode current collector. In the electrode body 30 as a wound electrode body, multiple such negative electrode tabs are stacked to form a group of negative electrode tabs (not shown). The group of negative electrode tabs is located on the other end side of the electrode body 30 in the Y direction (right end side in Figure 2) and is connected to the negative electrode current collector 32. Examples of materials used to construct the negative electrode current collector 32 include copper and copper alloys.

[0021] A separator is a component that insulates the positive electrode active material layer from the negative electrode active material layer. A porous resin sheet made of polyolefin resin is preferred as the separator. Examples of polyolefin resins include polyethylene (PE) and polypropylene (PP). A heat-resistant layer (HRL) containing an inorganic filler may be provided on the surface of the separator. Examples of constituent materials for the inorganic filler include alumina, boehmite, aluminum hydroxide, and titania.

[0022] As shown in Figures 1 and 2, the positive electrode terminal 40 is attached to the sealing plate 20. For example, the sealing plate 20 has a terminal opening that penetrates it in the thickness direction, and the positive electrode terminal 40 is attached to this opening with an insulating gasket between it and the sealing plate 20. A method for attaching the positive electrode terminal 40 to the sealing plate 20 is, for example, crimping. In this embodiment, the positive electrode terminal 40 is located in the Y direction between the narrow side surface 12 of the case body 10 and the gas discharge valve 20a. The positive electrode terminal 40 is exposed to the outside of the case C and also exposed to the inside of the case C. Inside the case C, the positive electrode terminal 40 is connected to the positive electrode current collector 31. The positive electrode terminal 40 is electrically connected to the electrode body 30 via the positive electrode current collector 31. Such a positive electrode terminal 40 is preferably made of metal, and more preferably of aluminum or an aluminum alloy.

[0023] The negative electrode terminal 50 is also attached to the sealing plate 20 (the attachment method is the same as described above for the positive electrode terminal 40). In this embodiment, the negative electrode terminal 50 is located in the Y direction between the narrow side surface 13 of the case body 10 and the gas discharge valve 20a. The negative electrode terminal 50 is exposed both to the outside of the case C and to the inside of the case C. Inside the case C, the negative electrode terminal 50 is connected to the negative electrode current collector 32. The negative electrode terminal 50 is electrically connected to the electrode body 30 via the negative electrode current collector 32. Such a negative electrode terminal 50 is preferably made of metal, and more preferably of copper or a copper alloy.

[0024] The electrolyte is housed inside the case C together with the electrode body 30. The electrolyte is impregnated into the electrode body 30. The electrolyte is typically a non-aqueous liquid electrolyte (non-aqueous electrolyte) containing a non-aqueous solvent and a supporting salt. The non-aqueous solvent contains carbonates such as ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). The supporting salt is, for example, a fluorine-containing lithium salt. Examples of fluorine-containing lithium salts include lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (F2LiNO4S2). Excess electrolyte that is not impregnated into the electrode body 30 may be stored inside the case C. Instead of such an electrolyte, a solid electrolyte (solid electrolyte) integrated with the electrode body 30 may be used.

[0025] Figure 3 is a flowchart showing an example of a method for manufacturing the energy storage device 100. The method for manufacturing the energy storage device 100 is an embodiment of the present invention and includes a component preparation step S1, an assembly step S2, and a welding step S3.

[0026] In the parts preparation process S1, various parts such as the case body 10, sealing plate 20, electrode body 30, positive electrode terminal 40, and negative electrode terminal 50 are prepared. The parts preparation process S1 includes the case body preparation process, the sealing plate preparation process, and the electrode body preparation process.

[0027] In the case body preparation process, a case body 10 having an opening 10A (a case body 10 having an opening 10A on at least one side) is prepared. For example, the case body 10 can be manufactured by drawing a metal plate.

[0028] In the sealing plate preparation process, a sealing plate 20 is prepared to close the opening 10A. In this process, the sealing plate 20 is prepared with the positive electrode terminal 40 and negative electrode terminal 50 attached. When attaching the electrode terminals (positive electrode terminal 40, negative electrode terminal 50), first, two openings for attaching the electrode terminals are formed in a rectangular flat plate for the sealing plate 20 by machining, such as drilling holes. Next, the electrode terminals (positive electrode terminal 40, negative electrode terminal 50) are attached to each opening in the flat plate, for example, by crimping.

[0029] The sealing plate 20 prepared in this process has a first surface 21, a second surface 22, and an outer peripheral edge 23, as shown in Figure 4 (in Figure 4, the positive electrode terminal 40 and negative electrode terminal 50, which are electrode terminals, are not shown). The first surface 21 is the surface of the sealing plate 20 that faces the opening 10A side of the case body 10. The second surface 22 is located on the opposite side from the first surface 21. The outer peripheral edge 23 surrounds the first surface 21 and the second surface 22. The sealing plate 20 also has a groove 22g on the second surface 22 along the outer peripheral edge 23. The groove 22g extends along the outer peripheral edge 23 around the entire circumference of the sealing plate 20. The distance d1 (shown in Figure 5) from the outer peripheral edge 23 to the groove 22g is, for example, 0.9 to 1.3 mm, and preferably 1.0 to 1.2 mm. Distance d1 is specifically the distance from the outermost edge of the outer peripheral edge 23 of the sealing plate 20 to the groove 22g in a direction perpendicular to the Z direction. The width of the groove 22g (the dimension in the groove 22g in a direction perpendicular to the elongation direction) is, for example, 0.3 to 0.7 mm, preferably 0.4 to 0.6 mm. The depth of the groove 22g (the length from the second surface 22 downward in the figure) is preferably 0.2 mm or more, more preferably 0.3 mm or more, and even more preferably 0.5 mm or more, from the viewpoint of suppressing heat diffusion to the side opposite to the outer peripheral edge 23 with respect to the groove 22g during laser irradiation. The depth of the groove 22g is preferably 0.7 mm or less, more preferably 0.65 mm or less, and even more preferably 0.6 mm or less, from the viewpoint of suppressing damage to the sealing plate 20. Examples of methods for forming the groove 22g include cutting, pressing, and etching.

[0030] In the electrode preparation process, the electrode body 30 is prepared. The electrode body 30 can be manufactured, for example, by stacking the above-mentioned separator (first separator), positive electrode, separator (second separator), and negative electrode in this order, and then winding the stacked material.

[0031] In assembly step S2, first, the positive electrode terminal 40 and negative electrode terminal 50 attached to the sealing plate 20 are electrically connected to the electrode body 30. Specifically, first, the positive electrode current collector 31 is connected to the group of positive electrode tabs (multiple stacked positive electrode tabs) on the electrode body 30, and the negative electrode current collector 32 is connected to the group of negative electrode tabs (multiple stacked negative electrode tabs). One example of a connection method is ultrasonic bonding. After that, the positive electrode terminal 40 and negative electrode terminal 50 attached to the sealing plate 20 are connected to the positive electrode current collector 31 and the negative electrode current collector 32, respectively. This results in an assembly in which the sealing plate 20, electrode body 30, positive electrode terminal 40, negative electrode terminal 50, etc. are assembled. One example of a connection method between the terminals and the current collectors is laser welding and crimping.

[0032] In assembly step S2, the electrode body 30 side of the assembly described above is inserted into the case body 10 through the opening 10A, and the sealing plate 20 is attached to the edge 10E of the case body 10 so as to close the opening 10A. A step (not shown) may be provided on the inner surface of the edge 10E of the case body 10 for positioning the sealing plate 20 in the Z direction. If such a step is provided on the edge 10E, the sealing plate 20 can be attached to the edge 10E so as to rest its peripheral edge on the step.

[0033] After such assembly process S2 and before the next welding process S3, the edge 10E of the case body 10 and its vicinity may be pressed against the outer peripheral edge 23 of the sealing plate 20 using a clamping jig. The clamping jig may include, for example, a pair of first clamps that press the edge 10E and its vicinity on a pair of narrow surfaces 12 and 13 in a direction perpendicular to the narrow surfaces 12 and 13, and a pair of second clamps that press the edge 10E and its vicinity on a pair of wide surfaces 14 and 15 in a direction perpendicular to the wide surfaces 14 and 15. With such a clamping jig, the edge 10E and its vicinity on the narrow surfaces 12 and 13 can be pressed against the sealing plate 20 or its outer peripheral edge 23 by the pair of first clamps, and the edge 10E and its vicinity on the wide surfaces 14 and 15 can be pressed against the sealing plate 20 or its outer peripheral edge 23 by the pair of second clamps. In the molded case body 10, in its natural state, a bulge tends to form outward, particularly in the center of the width direction Y of the wide surfaces 14 and 15. When the sealing plate 20 is attached to the opening 10A or edge 10E of such a case body 10, a gap tends to form between the case body 10 and the sealing plate 20. To address this, after attaching the sealing plate 20 to the edge 10E of the case body 10, the bulge can be corrected by pressing the edge 10E and its vicinity against the sealing plate 20 or outer edge 23 using a clamping jig. This makes it less likely for a gap to form between the case body 10 and the sealing plate 20. This helps to prevent welding spatter from laser welding in the next welding process S3 from passing through the gap between the case body 10 and the sealing plate 20 and entering the interior of the case body 10 or case C.

[0034] Next, in welding step S3, with the sealing plate 20 mounted on the case body 10 so that its first surface 21 faces the case body 10 and closes the opening 10A, the case body 10 and the sealing plate 20 are laser-welded using a predetermined laser welding device. Welding step S3 includes a first step and a subsequent second step.

[0035] In the first step, as shown in Figure 5, a laser beam L1 (first laser beam) is irradiated into the region between the outer peripheral edge 23 and the groove 22g of the sealing plate 20. The irradiation area (irradiation spot) of the laser beam L1 is scanned over the entire circumference of the sealing plate 20 by the laser irradiation device. The irradiation spot of the laser beam L1 is scanned to follow the planned irradiation line (along the outer peripheral edge 23) within the region. In the first step, at least a portion of the outer peripheral edge 23 of the sealing plate 20 is irradiated with the laser beam L1 and melted. As a result, in the first step, as shown in Figure 6, a melted and aggregated portion (temporarily melted portion Wa) is formed in the region from the outer peripheral edge 23 to the groove 22g of the sealing plate 20.

[0036] Examples of laser light L1 types from the perspective of the laser medium include semiconductor lasers, gas lasers, and solid-state lasers. Examples of semiconductor lasers include diode lasers (wavelength 1070 nm). Examples of solid-state lasers include fiber lasers (wavelength 1070 nm) and Nd:YAG lasers (wavelength 1064 nm). Examples of gas lasers include CO2 lasers (wavelength 10.6 μm). Examples of laser light L1 types from the perspective of the laser oscillation mode include continuous wave lasers (CW lasers) and pulsed lasers. Examples of laser light L1 types from the perspective of energy distribution include ring mode lasers, Gaussian lasers, and flat-top lasers. Examples of ring mode lasers include ring mode lasers of the type that include a center beam and a ring beam surrounding the center beam. A ring-mode laser is obtained, for example, by passing laser light from a laser oscillator through a two-layer optical fiber consisting of a center core and a ring core (at the tip of the optical fiber, the center beam is emitted from the center core and the ring beam is emitted from the ring core). As shown in Figure 7, the irradiation spot of the ring-mode laser has a center portion 71 and a ring portion 72 surrounding it. The center portion 71 is the irradiation spot of the center beam. The ring portion 72 is the irradiation spot of the ring beam. Such a ring-mode laser is suitable for forming a molten pool with a relatively gentle temperature distribution around a keyhole, while forming a keyhole of a desired depth at the irradiation point of the laser on the workpiece and in its vicinity. Forming a keyhole of a desired depth helps in forming a weld with sufficient welding depth. The gentle temperature distribution of the molten pool helps in stabilizing the molten pool (suppressing waviness), and therefore helps in suppressing the generation of welding spatter. The same applies to the type of laser light in terms of the laser medium and the type of laser light in terms of energy distribution, as described later for laser light L2.

[0037] The distance d2 from the outer peripheral edge 23 of the sealing plate 20 to the center of the irradiation spot of the laser beam L1 is, for example, 0.45 to 0.65 mm, preferably 0.50 to 0.60 mm. Specifically, distance d2 is the distance from the outermost edge of the outer peripheral edge 23 of the sealing plate 20 to the center of the irradiation spot of the laser beam L1 in a direction perpendicular to the Z direction. The ratio of distance d2 to distance d1 (d2 / d1) is preferably 0.40 or more, more preferably 0.45 or more, preferably 0.60 or less, and more preferably 0.55 or less, from the viewpoint of appropriately forming the molten portion Wa described above.

[0038] When a ring-mode laser is used as the laser beam L1, the diameter D1 of the center portion 71 of the ring-mode laser is, for example, 0.10 mm or more, preferably 0.20 mm or more, and more preferably 0.25 mm or more, from the viewpoint of securing the irradiation area of ​​the center beam and securing the formation size of the molten portion Wa described above. The diameter D1 of the center portion 71 is, for example, 0.50 mm or less, preferably 0.40 mm or less, and more preferably 0.35 mm or less, from the viewpoint of securing the energy density of the center beam and securing the formation size of the molten portion Wa described above. The diameter D2 of the ring portion 72 of the laser beam L1, which is a ring-mode laser, is, for example, 0.60 mm or more, preferably 0.70 mm or more, and more preferably 0.80 mm or more, from the viewpoint of stabilizing the molten portion described above. The diameter D2 of the ring portion 72 is, for example, 1.2 mm or less, preferably 1.1 mm or less, and more preferably 1.0 mm or less, from the viewpoint of preventing the case body 10 from melting in the vicinity of the molten portion Wa described above.

[0039] When a ring-mode laser is used as the laser beam L1, the laser power (laser output) of the center beam (center portion 71 in Figure 7) of the ring-mode laser is, for example, 800W or more, preferably 1000W or more, and more preferably 1200W or more, from the viewpoint of ensuring the amount of energy input by the center beam and ensuring the formation size of the molten portion Wa described above. From the viewpoint of suppressing laser glitches and welding spatter, the laser power of the center beam is, for example, 1500W or less, preferably 1400W or less, and more preferably 1300W or less. The laser power of the ring beam (ring portion 72 in Figure 7) of the ring-mode laser L1 is, for example, 3000W or more, preferably 3300W or more, and more preferably 3500W or more, from the viewpoint of ensuring the amount of energy input to the welding location. From the viewpoint of realizing heat conduction welding and stabilizing the molten pool, the laser power of the ring beam is, for example, 6000W or less, preferably 5000W or less, and more preferably 4000W or less.

[0040] The scanning speed (welding speed) of the laser beam L1 irradiation spot is preferably 150 mm / s or more, more preferably 180 mm / s or more, and even more preferably 200 mm / s or more, from the viewpoint of suppressing excessive energy input to the laser irradiation area. The scanning speed of the laser beam L1 irradiation spot is, for example, 300 mm / s or less or 250 mm / s or less.

[0041] In the second step of welding process S3, as shown in Figure 8, a laser beam L2 (second laser beam) is irradiated onto the boundary between the case body 10 and the sealing plate 20. The irradiation area (irradiation spot) of the laser beam L2 is scanned by the laser irradiation device over the entire circumference of the boundary between the case body 10 and the sealing plate 20. The center of the irradiation spot of the laser beam L2 is located on the case body 10. In the second step, the irradiation of the laser beam L2 causes the edge 10E of the case body 10 and the portion of the sealing plate 20 including the aforementioned molten portion Wa to melt and aggregate (integrate). Preferably, a keyhole is formed in the molten aggregate portion (keyhole welding). As a result, in the second step, as shown in Figure 9, a welded portion Wb is formed that joins the edge 10E of the case body 10 and the peripheral portion of the sealing plate 20.

[0042] When a ring-mode laser is used as the laser beam L2, the diameter D1 of the center portion 71 of the ring-mode laser is, for example, 0.10 mm or more, preferably 0.20 mm or more, and more preferably 0.25 mm or more, from the viewpoint of securing the irradiation area of ​​the center beam and securing the formation size of the weld Wb as described above. The diameter D1 of the center portion 71 is, for example, 0.50 mm or less, preferably 0.40 mm or less, and more preferably 0.35 mm or less, from the viewpoint of securing the energy density of the center beam and securing the formation size (including the welding depth) of the weld Wb. The diameter D2 of the ring portion 72 of the laser beam L2, which is a ring-mode laser, is, for example, 0.60 mm or more, preferably 0.70 mm or more, and more preferably 0.80 mm or more, from the viewpoint of securing the amount of energy input to the welding location. The diameter D2 of the ring portion 72 is, for example, 1.2 mm or less, preferably 1.1 mm or less, and more preferably 1.0 mm or less, from the viewpoint of realizing heat conduction welding and stabilizing the molten pool.

[0043] When a ring-mode laser is used as the laser beam L2, the laser power of the center beam (center portion 71 in Figure 7) of the ring-mode laser is, for example, 1500W or more, preferably 1700W or more, and more preferably 1800W or more, from the viewpoint of ensuring the amount of energy input from the center beam and ensuring the welding depth of the weld Wb described above. The laser power of the center beam is, for example, 2100W or less, preferably 2000W or less, and more preferably 1900W or less, from the viewpoint of ensuring the amount of energy input from the center beam and ensuring the formation size of the molten portion Wa described above. When both laser beams L1 and L2 are ring-mode lasers, it is preferable that the laser power of the center beam of laser beam L2 is greater than the laser power of the center beam of laser beam L1. The laser power of the ring beam (ring portion 72 in Figure 7) of laser beam L2, which is a ring-mode laser, is, for example, 3000W or more, preferably 3300W or more, and more preferably 3500W or more, from the viewpoint of maintaining a stable molten pool. From the viewpoint of suppressing laser glitches and welding spatter, the laser power of the ring beam is, for example, 6000W or less, preferably 5000W or less, and more preferably 4000W or less. The laser power of laser beam L2 is preferably greater than the laser power of laser beam L1.

[0044] The scanning speed (welding speed) of the laser beam L2 irradiation spot is preferably 150 mm / s or more, more preferably 180 mm / s or more, and even more preferably 200 mm / s or more, from the viewpoint of suppressing excessive energy input to the laser irradiation area. The scanning speed of the laser beam L2 irradiation spot is, for example, 300 mm / s or less or 250 mm / s or less.

[0045] On the planned welding line between the case body 10 and the sealing plate 20, the irradiation spot of laser beam L2 is scanned with a delay after the irradiation spot of laser beam L1. The delay time of the irradiation spot of laser beam L2 relative to the irradiation spot of laser beam L1 is preferably 10 milliseconds or more, more preferably 15 milliseconds or more, and even more preferably 20 milliseconds or more, from the viewpoint of ensuring the time required for the molten portion Wa described above to solidify. From the viewpoint of the manufacturing efficiency of the energy storage device 100, the delay time is preferably 50 milliseconds or less, more preferably 40 milliseconds or less, and even more preferably 30 milliseconds or less.

[0046] Through the welding process S3 described above, the edge 10E of the case body 10 and the sealing plate 20 are joined together over the entire area, forming an airtightly sealed case C.

[0047] After the welding process S3, an electrolyte injection process is performed in which electrolyte is injected into the case body 10, an aging process is performed in which the energy storage device 100 is left for a predetermined time after being charged, and an inspection process is performed to check for internal short circuits in the energy storage device 100 as appropriate. Specifically, in the electrolyte injection process, electrolyte is injected into the inside of the case body 10 through a predetermined injection hole. In this manner, the above-described energy storage device 100 can be manufactured.

[0048] The energy storage device 100 can be used for various applications. For example, the energy storage device 100 can be suitably used as a power source (driving power supply) for motors mounted on vehicles such as passenger cars and trucks. The type of vehicle is not particularly limited, but examples include plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs), and battery electric vehicles (BEVs).

[0049] The irradiation of laser light L1 in the above-described energy storage device manufacturing method is suitable for initially melting at least a portion of the surface of the outer edge 23 of the sealing plate 20 and for forming a melted and aggregated portion (pre-melted portion Wa) in the region from the outer edge 23 to the groove portion 22g of the sealing plate 20. By initially melting at least a portion of the surface of the outer edge 23, variations in the shape of the surface are reduced. At the same time, the melted portion created by the irradiation of laser light L1 in the said region tends to aggregate and round due to the action of surface tension acting on the melted portion in that region. The irradiation of laser light L2 after such irradiation of laser light L1 is suitable for forming a welded portion Wb with suppressed variations in welding depth at the boundary between the case body 10 and the sealing plate 20. Therefore, the above-described energy storage device manufacturing method is suitable for suppressing variations in welding depth caused by variations in the surface shape of the outer edge 23 of the sealing plate 20 during welding of the case body 10 and the sealing plate 20.

[0050] According to the inventors' knowledge, in laser welding of the boundary between the case body and the sealing plate with a single laser irradiation, variations in welding depth may occur at the welding point due to variations in the surface shape of the outer edge of the sealing plate (the abutting surface with respect to the case body) (for example, occurring during punching). For example, in the manufacturing process of the above-mentioned energy storage device 100, the boundary (around the entire circumference) between the case body 10 and the sealing plate 20 before welding may include a first boundary (where the gap opening towards the laser irradiation side between the outer edge 23 of the sealing plate 20 and the case body 10 is relatively large) as shown on the left side of Figure 10(a), and a second boundary (where the gap opening towards the laser irradiation side between the outer edge 23 of the sealing plate 20 and the case body 10 is significantly smaller than that of the first boundary) as shown on the right side of Figure 10(a). In this case, it is assumed that the boundary between the case body 10 and the sealing plate 20 is welded with a single laser irradiation. In a laser irradiation device, if the laser irradiation conditions are set to conditions suitable for the first boundary (first laser irradiation conditions) (i.e., conditions that allow the formation of a weld with an appropriate welding depth by laser irradiation to the first boundary), a weld with an appropriate welding depth Wb, as shown on the left side of Figure 10(b), is formed at the first boundary, whereas a weld with an insufficient welding depth Wb, as shown on the right side of Figure 10(b), is formed at the second boundary. The first laser irradiation conditions are too weak to form a weld with an appropriate welding depth Wb at the second boundary. On the other hand, in a laser irradiation device, if the laser irradiation conditions are set to conditions suitable for the second boundary (second laser irradiation conditions) (i.e., conditions that allow a weld with an appropriate welding depth to be formed by laser irradiation to the second boundary), a weld with an appropriate welding depth Wb, such as shown on the right side of Figure 10(c), is formed at the second boundary, whereas at the first boundary, a weld with an excessive welding depth Wb, such as shown on the left side of Figure 10(c), is formed. The second laser irradiation conditions are too strong to form a weld with an appropriate welding depth Wb at the second boundary (for example, a through keyhole is formed during laser irradiation).In contrast to these, in the welding process S3 described above, at least a portion of the surface of the outer edge 23 of the sealing plate 20 is melted by irradiating the area between the outer edge 23 and the groove 22g with laser light L1 to prepare the surface shape, and then the case body 10 and the sealing plate 20 are welded by irradiating the boundary between the case body 10 and the sealing plate 20 with laser light L2, thereby suppressing variations in welding depth.

[0051] In welding step S3, each of the laser beams L1 and L2 is preferably a ring-mode laser including a center beam and a ring beam surrounding the center beam. Such a configuration is suitable for suppressing a rapid rise in temperature at the laser irradiation spot scanned along the planned laser irradiation line for each of the laser beams L1 and L2, and therefore is suitable for suppressing the generation of welding spatter during laser irradiation.

[0052] In welding step S3, preferably, the laser power of laser beam L2 is greater than the laser power of laser beam L1 (first configuration). When both laser beams L1 and L2 are ring mode lasers, preferably, the laser power of the center beam of laser beam L2 is greater than the laser power of the center beam of laser beam L1 (second configuration). The portion of the sealing plate 20 that is melted and formed by irradiation with laser beam L1 (pre-melted portion Wa) has a glossy surface, so the laser light is less absorbed in that portion than before it melted. The above first and second configurations regarding laser power help to ensure the absorption rate or energy input of laser beam L2 at the boundary between the edge portion 10E of the case body 10 and the sealing plate 20, and therefore help to ensure a sufficient welding depth for the weld portion Wb formed in welding step S3.

[0053] The welding process S3 may be carried out using a first laser irradiation device for irradiating laser beam L1 and a second laser irradiation device for irradiating laser beam L2. With such a configuration, the laser irradiation conditions and laser irradiation locations for each of the laser beams L1 and L2 can be controlled individually. Alternatively, the welding process S3 may generate laser beams L1 and L2 by splitting a single laser beam into two laser beams (a laser irradiation device of that nature may be used).

[0054] Figure 11 shows an example of an optical system for splitting laser light. The optical system shown in Figure 11 (first optical system) comprises a collimator lens 201, a beam splitter 202, galvanometer mirrors 203 and 204, and a focusing lens 205. These constitute, for example, a laser scanning unit and are housed in a housing 206. The housing 206 has a laser output port 206a. In the first optical system, the laser light LS emitted from a laser oscillator (not shown) and guided to the first optical system via an optical fiber FB is first collimated by the collimator lens 201. Next, the laser light is split by the beam splitter 202 into the aforementioned laser light L1 and laser light L2 (in Figure 11, laser light L2 is shown with a thick line). The beam splitter 202 is, for example, a diffractive optical element (DOE) splitter. Next, the laser beams L1 and L2 are reflected by the galvanometer mirror 203 and 204, respectively, and then focused by the focusing lens 205 and irradiated onto the object (each laser beam is emitted outside the housing 206 through the laser output port 206a). The galvanometer mirrors 203 and 204 each have a mirror surface, and their oscillation angle around a single rotation axis is controlled by a galvanometer motor (not shown), and this control controls the direction of light reflection on the mirror surface (the same applies to the galvanometer mirrors described later). The scanning of each irradiation spot of the laser beams L1 and L2 is controlled by controlling the individual light reflection directions of the galvanometer mirrors 203 and 204. In the welding process S3 described above, such a first optical system may be used to split a single laser beam from a light source into two laser beams to generate laser beams L1 and L2.

[0055] Figure 12 shows another example of an optical system for splitting laser light. The optical system shown in Figure 12 (second optical system) comprises a collimator lens 301, a half mirror 302, galvanometer mirrors 303, 304, a focusing lens 305, a mirror 306, galvanometer mirrors 307, 308, and a focusing lens 309. These constitute, for example, a laser scanning unit and are housed in a housing 310. The housing 310 has a laser output port 310a. In the second optical system, the laser light LS emitted from a laser oscillator (not shown) and guided to the second optical system via an optical fiber FB is first collimated by the collimator lens 301. Next, the laser light LS is split by the half mirror 302 into the aforementioned laser light L1 (light passed through the half mirror) and laser light L2 (light reflected from the half mirror). The laser beam L1 is reflected by galvanometer mirror 303 and galvanometer mirror 304, then focused by focusing lens 305, and irradiated onto the object through the laser output port 310a. The scanning of the irradiation spot of the laser beam L1 is controlled by controlling the individual light reflection directions of galvanometer mirrors 303 and 304. On the other hand, the laser beam L2 is reflected by mirror 306 toward galvanometer mirror 307, then reflected by galvanometer mirror 307 and galvanometer mirror 308, then focused by focusing lens 309, and irradiated onto the object through the laser output port 310a. The scanning of the irradiation spot of the laser beam L2 is controlled by controlling the individual light reflection directions of galvanometer mirrors 307 and 308. In the welding process S3 described above, such a second optical system may be used to split one laser beam from the light source into two laser beams, generating laser beams L1 and L2.

[0056] The technologies disclosed herein have been described in detail above. Unless otherwise specified, the embodiments and other details mentioned herein do not limit the present invention. Furthermore, the technologies disclosed herein can be modified in various ways, and each component and each process mentioned herein may be omitted or combined as appropriate, unless no particular problems arise. This specification also includes the disclosures described in the following sections.

[0057] Section 1: A step of preparing a case body having an opening on at least one side, A step of preparing a sealing plate to close the aforementioned opening, The process includes a welding step of laser welding the case body and the sealing plate while the sealing plate is attached to the case body so as to close the opening, The sealing plate prepared in the step of preparing the sealing plate has a first surface, a second surface opposite to the first surface, and an outer peripheral edge surrounding the first and second surfaces, and has a groove along the outer peripheral edge on the second surface. A method for manufacturing an energy storage device, wherein the welding step includes irradiating a first laser beam between the outer peripheral edge and the groove of the sealing plate while the sealing plate is mounted on the case body with its first surface facing the case body and closing the opening, and then irradiating a second laser beam at the boundary between the case body and the sealing plate.

[0058] Section 2: The method for manufacturing an energy storage device according to item 1, wherein the laser power of the second laser beam is greater than the laser power of the first laser beam.

[0059] Section 3: A method for manufacturing an energy storage device according to claim 1 or 2, wherein each of the first laser beam and the second laser beam is a ring-mode laser comprising a center beam and a ring beam surrounding the center beam.

[0060] Section 4: The method for manufacturing an energy storage device according to item 3, wherein the laser power of the center beam of the second laser beam is greater than the laser power of the center beam of the first laser beam.

[0061] Section 5: A method for manufacturing an energy storage device according to any one of claims 1 to 4, wherein in the step of laser welding the case body and the sealing plate, one laser beam is split into two laser beams to generate the first laser beam and the second laser beam. [Explanation of Symbols]

[0062] 100 Energy Storage Devices C Case 10 Case body 10A aperture 20 Sealing plate 21 Page 1 22 Side 2 22g groove 23 Outer edge 30 Electrode body 31 Positive electrode current collector 32 Negative electrode current collector 40 Positive terminal 50 Negative terminal S1 Parts preparation process S2 Assembly process S3 Welding Process Wa (Once melted) Wb weld

Claims

1. A step of preparing a case body having an opening on at least one side, A step of preparing a sealing plate to close the aforementioned opening, The process includes a welding step of laser welding the case body and the sealing plate while the sealing plate is attached to the case body so as to close the opening, The sealing plate prepared in the step of preparing the sealing plate has a first surface, a second surface opposite to the first surface, and an outer peripheral edge surrounding the first and second surfaces, and has a groove along the outer peripheral edge on the second surface. A method for manufacturing an energy storage device, wherein the welding step includes irradiating a first laser beam between the outer peripheral edge and the groove of the sealing plate while the sealing plate is mounted on the case body with its first surface facing the case body and closing the opening, and then irradiating a second laser beam at the boundary between the case body and the sealing plate.

2. The method for manufacturing an energy storage device according to claim 1, wherein the laser power of the second laser beam is greater than the laser power of the first laser beam.

3. The method for manufacturing an energy storage device according to claim 1, wherein each of the first laser beam and the second laser beam is a ring-mode laser including a center beam and a ring beam surrounding the center beam.

4. The method for manufacturing an energy storage device according to claim 3, wherein the laser power of the center beam of the second laser beam is greater than the laser power of the center beam of the first laser beam.

5. A method for manufacturing an energy storage device according to any one of claims 1 to 4, wherein in the step of laser welding the case body and the sealing plate, one laser beam is split into two laser beams to generate the first laser beam and the second laser beam.

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